This invention relates generally to loudspeaker systems and particularly to a system in which the loudspeakers are arranged in an enclosure in such a fashion as to minimize vibration of the enclosure.
The vibrational forces caused by the loudspeaker cone excursion are greatest for the lower frequencies. For example, if the cone is moving a quarter of an inch at 60 Hz., the cone assembly is being subjected to an acceleration of 49.3 gees. Common in the prior art is a loudspeaker system for low frequency reproduction, generally known as a subwoofer, including an enclosure with a single driver or two drivers mounted side by side. This unit can be free standing or it may be mounted in the ceiling, floor or walls. The loudspeaker cone assembly is mounted in one wall of the enclosure and moves in one direction causing an equal and opposite force to act upon the loudspeaker enclosure. When a subwoofer is mounted in the enclosure, these forces are of a great magnitude since subwoofers are responsive to the lower acoustic frequencies and the larger the loudspeaker, the greater the vibrations due to the greater mass and longer piston stroke.
One major disadvantage to this loudspeaker assembly is the excessive and unwanted vibration in and to adjoining rooms. Loudspeaker enclosures generally weigh much more than the cone assembly and are usually made of solid material, such as wood, in which sound travels more efficiently, faster and further. The enclosure does not move so far but there is as much total energy in the enclosure as in the cone assembly. When a wooden enclosure is attached to the frame of a house, the vibrations from the lower frequencies are easily transmitted through the entire house without the higher frequencies being heard. Since many people enjoy the aesthetics of a speaker system that is recessed, these people are left with a system that vibrates throughout the house and disturbs other people.
Also with prior art loudspeaker systems, the enclosure is normally placed in out of way places such as in corners, on top of bookshelves or behind drapes because with the excessive vibrations the enclosure is unable to serve other functions, for example, as an end table or a lamp stand. If an object is placed on these enclosures, the object will move or walk across the surface.
The ported system is a prior art approach which improves upon the acoustic suspension system and such a system is disclosed in U.S. Pat. No. 4,549,631. In the ported system there is an enclosure, a woofer and a port tube that can be used to alter the frequency response. In this system, the mass of air in the port reacts with the volume of air in the enclosure to create a port resonance and at the port resonance, the loudspeaker cone excursion is reduced. With this system there are still vibrations, especially at the lower frequencies, and the enclosure is unable to serve other functions such as an end table.
The present invention solves these and other problems in a manner not disclosed in the known prior art.